This invention relates to enrichment apparatus for an internal combustion engine. More particularly, this invention relates to engine enrichment apparatus which is thermally responsive and, in some embodiments, also centrifugally responsive.
Centrifugally-responsive compression release apparatus are known for internal combustion engines. A typical centrifugally-responsive compression release apparatus has a curved saddle member that is pivotable on a cam shaft of the engine. At least one flyweight is disposed on an end of the curved saddle. Another portion of the curved saddle has a cam member which, at low engine speeds, is positioned to engage the cam follower of an intake or exhaust valve, and to slightly lift the valve.
The purpose of such prior art compression release mechanisms is to increase engine startability. If one of the engine valves is slightly unseated during engine starting, the compression in the combustion chamber is reduced when the piston moves toward top dead center, thereby decreasing the force applied to the piston surface by the compressed gas in the combustion chamber.
Another purpose of the prior art compression release apparatus is as a secondary enrichening device to enrich the air/fuel mixture during engine starting, in addition to a primary enrichening device such as a primer or choke. These compression release devices enrich the air/fuel mixture only if the intake valve is partially unseated during the compression stroke of the engine. If a typical prior art compression release device is used with the intake valve, the typical air/fuel ratio during engine starting using the compression release is about 10-11:1, but the air/fuel ratio without the compression release engaged is about 11-13:1.
A significant disadvantage of a typical centrifugally-responsive compression release apparatus is that the compression release apparatus is disengaged before the engine is warmed up. The compression release apparatus is disengaged as soon as a predetermined speed of the engine has been reached, which is typically near the engine operating speed. However, the engine operating speed is reached in a few seconds or less after engine starting, long before the engine is warmed up. As soon as the compression release apparatus is disengaged, the enrichening due to the compression release ends, and the air/fuel mixture returns to a leaner ratio of about 11-13:1. If the engine is still cold, this leaning of the air/fuel ratio may cause the engine to stumble or stall.